The magnetic reconnection height of the mini flare at the jet base is very important parameter to probe about the reconnection mechanism. When jets are observed over the limb the reconnection point is clearly visible in the corona (e.g 10 Mm in the case of [1]}). For events occurring on the disk it is difficult to derive the altitude of reconnection. [2]}, [3]} and [4]} used a NLTE radiative transfer code in a 1D atmosphere model to derive the altitude of formation of the reconnection in UV burst visible in Mg II lines. The altitude range spans the high photosphere and chromosphere (50 to 900 km). With IRIS it was also found in UV bursts or IRIS bombs (IBs) that cool plasma emitting in chromospheric lines could overlay hotter plasma at Si IV line temperature [5]}. After a long debate about the temperature of the Si IV lines in possibly non equilibrium state, 3D simulation based on Bifrost code [6]} coupled with the MULTI3D code [7]} succeeded to mimic the large observed Si IV profiles (very similar to our UV Si IV burst) and the extended wing of the Ca K line with synthetic profiles both formed at different altitudes simultaneously due to an extended vertical current sheet in a strong magnetized atmosphere [8]}. They proposed that “the current sheet is located in a large bubble of emerging
magnetic field, carrying with it cool gas from the photosphere”.
This scenario is certainly valid for our observations.
We attempted to compute the optical thickness and the electron density in the mini flare area during the reconnection process [9]}, [10]}. The transition lines (Si IV and O IV) usually used for such estimations had so perturbed profiles that no reliable numbers could be put forward at the time of the reconnection. One minute later the Si IV lines were estimated to be nearly optical thin and the computed electron density arises to log(\(N_{\text{e}}\)  [cm\(^{-3}\) ]) = 11 \(\pm \)  0.3, value which corresponds to a plage or bright point, similarly in the paper of [11]}.
